Wireless communications is becoming increasingly important, with wireless systems finding their way into every growing numbers of applications. Wireless systems are become ubiquitous in the military environment.
In many wireless systems, it is desirable to provide two-way communications. Two way communications can be achieved through so-called frequency-division duplex operation. In the case of frequency-division duplex, two different frequencies are used, wherein a terminal can simultaneously (continuously) transmit on one frequency while receiving on the other frequency. For example, in a hub and spoke network, a hub terminal typically transmits on a first frequency and receives on a second frequency. The spoke terminals thus receive on the first frequency and transmit on the second frequency. Accordingly, the spoke terminals can each directly communicate with the hub terminal, but not with each other.
For hub and spoke terminals, frequency-division duplex operation is an acceptable way of providing full duplex communications. Frequency-division duplex is difficult to apply in other network types. For example, a set of terminals which are all configured to receive on the first frequency and transmit on the second frequency cannot establish direct communications with each other. Thus, frequency-division duplex is difficult to apply in a mesh network. While terminals can be split into two different types, e.g. a first terminal type (“type A”) which transmits on the first frequency and receives on the second frequency and a second terminal type (“type B”) which transmits on the second frequency and receives on the first frequency. Thus, type A terminals can directly communicate with type B terminals (and vice versa). Type A terminals cannot, however, communicate directly with other type A terminals, and type B terminals cannot communicate directly with other type B terminals. This can present difficulty, for example, when there are not enough of a particular type of terminal to provide the desired connectivity in a network, or when terminals move around resulting in a changing network topology. The different types of terminals are sometimes referred to as “genders” and the difficulties associated with having two different terminal types is sometimes referred to as the “gender problem.”
An alternative to frequency-division duplex is time-division duplex, where all transmissions occur on the same frequency. Time is shared between the transmitter and receiver, with the transmitter and receiver taking turns at (discontinuously) transmitting/receiving bursts of data. While time-division duplex can reduce gender problems, time-division-duplex has several other disadvantages. Because time division duplex data must be burst at a higher rate, this translates into lower communication range for a given transmission power. In addition, timing must be coordinated between different terminals to ensure that the transmission and reception intervals are properly synchronized. Furthermore, two terminals which are scheduled to transmit in the same time interval cannot communicate directly.
Accordingly, it has been recognized by the present inventors that there is a need for improved duplexing techniques.